man > btrfs-rescue(8)

BTRFS-RESCUE(8)                                 BTRFS                                BTRFS-RESCUE(8)

NAME
       btrfs-rescue - recover a damaged btrfs filesystem

SYNOPSIS
       btrfs rescue <subcommand> <args>

DESCRIPTION
       btrfs rescue is used to try to recover a damaged btrfs filesystem.

SUBCOMMAND
       chunk-recover [options] <device>
              Recover the chunk tree by scanning the devices

              Options

              -y     assume an answer of yes to all questions.

              -h     help.

              -v     (deprecated) alias for global -v option

       NOTE:
          Since  chunk-recover  will scan the whole device, it will be very slow especially executed
          on a large device.

       fix-device-size <device>
              fix device size and super block total bytes values that do not match

              Kernel 4.11 starts to check the device size more strictly and this might mismatch  the
              stored  value  of  total  bytes. See the exact error message below.  Newer kernel will
              refuse to mount the filesystem where the values do not match.  This error is not fatal
              and can be fixed.  This command will fix the device size values if possible.

                 BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528

              The mismatch may also exhibit as a kernel warning:

                 WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]

       clear-ino-cache <device>
              Remove leftover items pertaining to the deprecated inode cache feature.

              The inode cache feature (enabled by mount option "inode_cache")  has  been  completely
              removed in 5.11 kernel.

       clear-space-cache <v1|v2> <device>
              Completely remove the on-disk data of free space cache of given version.

              Especially  for  v1  free  space cache, clear_cache mount option would only remove the
              cache for updated block groups, the remaining would not be removed.  Thus this command
              is provided to manually clear the free space cache.

       clear-uuid-tree <device>
              Clear UUID tree, so that kernel can re-generate it at next read-write mount.

              Since kernel v4.16 there are more sanity check performed, and  sometimes  non-critical
              trees  like UUID tree can cause problems and reject the mount.  In such case, clearing
              UUID tree may make the filesystem to be mountable again  without  much  risk  as  it's
              built from other trees.

       super-recover [options] <device>
              Recover bad superblocks from good copies.

              Options

              -y     assume an answer of yes to all questions.

              -v     (deprecated) alias for global -v option

       zero-log <device>
              clear the filesystem log tree

              This  command will clear the filesystem log tree. This may fix a specific set of prob‐
              lem when the filesystem mount fails due to the log replay. See below for sample  stack
              traces that may show up in system log.

              The  common  case where this happens was fixed a long time ago, so it is unlikely that
              you will see this particular problem, but the command is kept around.

              NOTE:
                 Clearing the log may lead to loss of changes that were made since the last transac‐
                 tion commit. This may be up to 30 seconds (default commit period) or  less  if  the
                 commit was implied by other filesystem activity.

              One can determine whether zero-log is needed according to the kernel backtrace:

                 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
                 ? walk_log_tree+0x9c/0x19d [btrfs]
                 ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
                 ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
                 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
                 ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
                 ? open_ctree+0xff6/0x132c [btrfs]

              If  the  errors  are like above, then zero-log should be used to clear the log and the
              filesystem may be mounted normally again. The keywords to look  for  are  'open_ctree'
              which  says  that it's during mount and function names that contain replay, recover or
              log_tree.

EXIT STATUS
       btrfs rescue returns a zero exit status if it succeeds. Non zero is returned in case of fail‐
       ure.

AVAILABILITY
       btrfs   is   part   of   btrfs-progs.     Please    refer    to    the    documentation    at
       https://btrfs.readthedocs.io.

SEE ALSO
       btrfs-check(8), btrfs-scrub(8), mkfs.btrfs(8)


6.6.3                                       Mar 31, 2024                             BTRFS-RESCUE(8)